This invention relates to methods and apparatus for controlling a load, and more particularly, to methods and apparatus for controlling a load with a sensor wherein the sensor is responsive not only to a condition to be sensed but also to an enabling or disabling of the load.
The automatic control of loads, for example illumination systems, operated by AC or DC networks through the use of sensors is well known. Thus, highly convenient arrangements have been developed, for instance, wherein infrared sensors are employed to control an illumination system under conditions where an individual's entry into a room equipped with such a system results in the illumination system being automatically actuated. When the person leaves the room, the illumination system is again extinguished.
If the infrared sensor employed in such a system is a low-sensitivity device requiring that it be located at a relatively confined point of entry and exit, such a system may be operated without difficulty. However, when the sensitivity of the infrared sensor employed is increased to accommodate more generalized applications, such an increase in sensitivity will invariably result in the sensor's operation being adversely effected by switching of the controlled load which, in the case being discussed, is an illumination system. Thus it will be seen that when such a control arrangement employs a high-sensitivity infrared sensor it will be activated when an individual comes into the long range of the sensor. However, as soon as the illumination system is activated, the very activation thereof may be sensed to cause again a deactivation of the illumination system. Furthermore, in systems of this type when the sensitivity of the sensor is increased by way of amplification or the like, feedback of load transients and/or spikes on the electrical supply associated with the switching of the load may also result in uncontrolled possibly oscillatory switching of the load as a function of the sensor being employed. This is highly disadvantageous and has generally rendered such highly sensitive switching arrangements impractical.
Ordinarily, the infrared sensors employed in such systems are operated in a manner that the same are responsive to signal changes rather than stationary signal conditions. Therefore, those of ordinary skill in the art will readily appreciate that infrared sensors which are relatively sensitive are greatly subject to erroneous operation during intervals when an illumination load, for example, is being switched on, and conversely when the same is being switched off. More particularly, in an illumination system of the type being described, it will be appreciated that the system should switch on when an individual walks into a room and switch off when the individual leaves the room. However, during the time interval when the individual is in the room and the illumination system is on, normal activities of that individual within the room should cause the infrared sensor to keep the illumination on.
Ideally, when a lighting system is switched on by an infrared sensor, a first time interval should be imposed on that sensor during which transients generated by the actuation of the load will not cause spurious switching. This interval should exceed the interval of transient conditions associated with the load. Furthermore, once the interval of transient conditions associated with the load has expired, the sensed conditions which may well be associated with the movement of an individual within the range of the sensor are employed solely for an extension of the period of illumination and switching associated with turning off of the light only occurs when no signal changes have occurred within a given time span additionally or alternatively. Once the illumination system has been switched off, any detection of a sensed condition should again energize the system, but a zone which avoids transient switching associated with a turning off of the load must also be established.
When it is desired to convert an existing illumination system which is typically manually switched to an electronic system employing infrared sensors, further difficulty is typically encountered. More particularly, such systems are generally actuated through the presence of a manual switch connected in series with the lighting load and no neutral conductor is usually present. Therefore, in altering such a manual system to employ electronic switching, great difficulties are encountered in developing techniques for providing the supply voltage already in place to the electronics which are being introduced for purposes of switching. As no neutral conductor is normally installed and only one switch-interrupted conductor to the load, a way has to be found to develop a DC-supply voltage from these conditions for installation. Thus, those of ordinary skill in the art will appreciate that when a manually switched system is to be converted to an electronically sensed system it is most desirable that such changeover be provided without a need for substantial modifications in the wiring already in place.
Therefore, it is a principal object of the present invention to provide methods and apparatus for controlling a load switched by a sensor.
An additional object of the present invention is to provide methods and apparatus for avoiding spurious switching on and/or off a load controlled by an infrared sensor.
A further object of the present invention is to provide techniques for converting existing manually switched loads to sensor controlled switching without the introduction of substantial wiring changes in the existing system.
Various other objects and advantages of the present invention will become clear from the following description of several exemplary embodiments thereof and the novel features will be particularly pointed out in conjunction with the claims appended hereto.